1. Field of the Invention
The present invention relates to a particle-beam treatment system in which, in the case where, during particle-beam irradiation, multi-layer conformal irradiation is performed while setting of the shape (leaf position) of a multileaf collimator in an irradiation head is changed, the shape of the multileaf collimator is detected by a leaf-position detection mechanism, and more particularly to a particle-beam treatment system in which, during particle-beam irradiation, the shape of the multileaf collimator can be monitored.
2. Description of the Related Art
In a particle-beam treatment system that performs multi-layer conformal irradiation, the dose to be administered to a patient and the distribution thereof are spatially divided and then delivered, so that the dose delivery is made optimal for the shape of a target. The dose distribution divided and delivered in this manner depends on the setting of the irradiation system, such as setting of the shape of the multileaf collimator and the like, and the setting condition of the patient position. In the case where, during particle-beam irradiation, the shape of the multileaf collimator or the patient position is changed from the shape or the setting position that have been decided in a treatment plan, the dose to be administered and the dose distribution differ from those in the treatment plan; therefore, it is required to immediately stop the particle-beam irradiation. For this reason, the monitoring (ascertainment) of the shape (leaf position) of the multileaf collimator and the patient position is an important function for delivering to the patient the dose distribution that has been prescribed in a treatment plan; thus, redundancy and multiplicity are required in the foregoing monitoring.
In the case where, in a particle-beam treatment, a static irradiation, which has been practiced since the time before the advent of the multi-layer conformal irradiation, was performed, the shape of the multileaf collimator was ascertained immediately prior to the particle-beam irradiation, based on a light-irradiation field, formed by a light localizer, and X-ray radiographing; then, it could be secured, through detection by use of a detector incorporated in the multileaf collimator, that the forgoing shapes did not change during irradiation. In addition, the conventional monitoring and ascertainment of a patient position were visually performed by shooting a marker written on the surface of the patient body and the projected image of a laser pointer, through a video camera mounted on the ceiling or the sidewall of the treatment room.
FIG. 8 is a conventional system block diagram illustrating a method of monitoring and ascertaining the shape of a multileaf collimator and a patient position in the case where a static irradiation, which has been practiced since the time before the advent of the multi-layer conformal irradiation, is performed. FIG. 9 is a configuration diagram illustrating the structure and the system of a typical multileaf collimator. In the conventional static particle-beam treatment, the ascertainment of the shape (leaf position) of a multileaf collimator has been performed by observing, immediately prior to the irradiation, the light-irradiation field formed by a light localizer 11 and the image, of a digital radiograph (DR) 19, which is radiographed, with a X-ray source 13 movably provided on the beam axis, in addition to automatic comparison performed by a leaf-position detection mechanism (e.g., the position is detected by use of an encoder) incorporated in the multileaf collimator. In some cases, a particle-beam flatness monitor is further utilized. In addition, the X-ray source 13 moves on a monitor drive stand 51 that is provided in such a way as to be separated from and to be on a multileaf collimator 14; thus, the X-ray source 13 can be disposed on the beam axis.
Explanations therefor will be made with reference to FIGS. 8 and 9. In FIG. 8, reference characters 1, 2, 2a, 2b, 3, 4, 5, and 6 denote an irradiation head, a patient, a diseased site of the patient, a patient-position marker, a particle beam, a dose monitor, wobbler magnets, and a scatterer, respectively; reference characters 7, 8, 9, 10, 11, 12, 13, 14, and 14a denote a ridge filter, a range shifter, an irradiation-system control computer, an irradiation-head control device, alight localizer, a mirror, an X-ray source, a multileaf collimator, and a multileaf-collimator control device, respectively; reference characters 15, 16, 17a, 18, 19, 20, 20a, and 51 denote a patient-monitoring video camera, a video-camera controller, an image monitor, a treatment table, a DR, a laser pointer, a laser beam, and a monitor drive stand, respectively.
In FIG. 9, reference characters 14a, 14b, 21, 22, 23, 24, 25, 26, 27, and 28 denote a multileaf collimator control device, a multileaf collimator head unit, a shape of a multileaf collimator, a collimator leaf, a leaf drive mechanism, a mechanical stopper, a leaf-position detector, a leaf drive unit, a signal processing circuit, and a collimator manipulation unit, respectively. The particle beam 3 accelerated by a particle-beam accelerator is led by a beam transport system to the irradiation head 1, limited by the multileaf collimator 14 to a necessary irradiation region, and then irradiated onto the patient 2.
The ascertainment of the shape (leaf position) 21 of the multileaf collimator has been performed by, immediately prior to the irradiation, disposing the light localizer 11 and the mirror 12 at the upstream side of the multileaf collimator 14, thereby visually ascertaining the multileaf-collimator shape which is projected onto a plane perpendicular to the traveling direction of the particle beam, in addition to performing automatic comparison and ascertainment of the respective output information items of the position-detection mechanisms 25 for the corresponding collimator leaves and the original setting information in the treatment plan; furthermore, the shape 21, of the multileaf collimator, which is X-rayed with the X-ray digital radiograph (DR) 19 with the X-ray source 13 movably arranged on the beam line, has been ascertained. Additionally, in the conventional monitoring of a patient position, the patient-position marker 2b written on the surface of the patient body and the light marker (e.g., a cross line), which is obtained by projecting, onto the surface of the patient body, the laser beam 20a from the laser pointer 20 provided on the sidewall or the ceiling of the treatment room, have been shot by the video camera 15 that is also disposed on the sidewall or the ceiling of the treatment room and ascertained on the image monitor 17a. In addition, the technical literatures for this field include the following documents:
Patent Document 1: Japanese Patent Application Laid-Open No. 1989-274741
Patent Document 2: Japanese Patent Application Laid-Open No. 1990-182273
Patent Document 3: Japanese Patent Application Laid-Open No. 1994-246015
Patent Document 4: U.S. Pat. No. 4,882,741 (corresponding Japanese publication: Japanese Patent Application Laid-Open No. 1989-146564)
Patent Document 5: GB Patent No. 2,211,710A (corresponding Japanese publication: Japanese Patent Application Laid-Open No. 1989-146564)
Non-patent Document 1: PHYSICS Annual Report 2001-2002, 4. Improvement of the HIMAC Treatment System with the Layer-Stacking Conformal Irradiation Method, Nobuyuki Kanematsu, et al.
In a conventional static irradiation method utilizing a particle-beam treatment system, as illustrated in FIG. 8, the monitoring and the ascertainment of the shape of a multileaf collimator has been performed by visually ascertaining, immediately prior to irradiation, the light-irradiation field formed by the light localizer 11 and the mirror 12 that are disposed at the upstream side of the multileaf collimator and observing the image, of the digital radiograph (DR) 19, which is radiographed with the X-ray source 13 disposed on the beam axis, in addition to automatic comparison performed by leaf-position detection mechanisms incorporated in the multileaf collimator; however, because, the ascertainment work in a treatment room is involved, the foregoing methods, except for the method of ascertainment performed by the leaf-position detection mechanisms incorporated in the multileaf collimator, cannot be applied to a dynamic irradiation method such as the multi-layer conformal irradiation in which the setting for a multileaf collimator is changed during irradiation. Moreover, because the space above the monitor drive stand 51 is limited, it is difficult to provide additional reinforcement. Still moreover, the conventional monitoring of a patient position has been performed by shooting the marker 2b written on the surface of the patient body and the image of the laser pointer 20, through the video camera 15 mounted on the ceiling or the sidewall of the treatment room, thereby carrying out visual ascertainment on the image monitor 17a; however, in some cases, the monitoring subject has not securely been captured, depending on the irradiation arrangement.
It is possible in principle to make the leaf-position detector 25 multiple and redundantly ascertain the shape 21 of the multileaf collimator, in order to ascertain the setting condition during particle-beam irradiation; however, the multileaf collimator has a great number of drive elements and the space where the newly added leaf-position detectors and signal transmission paths are mounted in the multileaf collimator head unit is limited, whereby many difficult issues exist. Furthermore, in contrast to the conventional static irradiation method, in the multi-layer conformal irradiation, a dose is administered to a treatment target that is divided into a plurality of irradiation units; therefore, a change in the patient position during particle-beam irradiation forms high-dose and low-dose regions in the dose distribution.
The foregoing issue cannot be addressed with the setting margin, for the target, which is set in accordance with the conventional static irradiation method and in consideration of the change of the body position; thus, nothing but improvement in the fixing method for the fixing device and the like and more stringent monitoring of body-position change can serve as measures for the foregoing issue. In the conventional monitoring through the video camera 15 disposed on the sidewall or the ceiling of a treatment room, a dead angle or the like, which may be caused depending on the irradiation arrangement, may make it difficult to securely monitor the body position that is subject to irradiation.